Spring assemblies of this general type are disclosed in U.S. Pat. No. 3,047,280. Also described is their use in connection with hinge mechanisms such as for instance the hinges supporting the tail gate, boot lid (or trunk lid) or bonnet (or hood) of an automobile.
Automobile boot lids and tail gates are conventionally mounted on hinges which are biassed to the open position by gas struts. As compared to springs, gas struts have a number of known disadvantages. A major problem is that the force which they exert varies substantially according to the ambient temperature.
Springs do not suffer from this disadvantage but previous proposals for the use of springs in supporting components of this nature have also encountered practical difficulties. Helical coil springs and torsion bars have been proposed but these often encroach into the usable space of the luggage storage area to a significant extent. The type of coil strip spring assembly described in U.S. Pat. No. 3,047,280 once installed avoids all these past disadvantages in that it is compact and insensitive to variations of ambient temperature.
However, despite the fact the use of these types of spring assemblies in this particular context was proposed as long ago as 1962 in U.S. Pat. No. 3,047,280 they have not been used to any significant extent in automobile manufacture.
The process of installation of a spring of this type into an automobile boot by way of example to construct such an installation would involve the attachment to one component of the hinge in situ in the boot of an arcuate support member such as part of a drum to which is secured one end of a multileaf coiled strip spring. An abutment member will be provided on another component of the hinge moveable with respect to the location for the arcuate support member and it will be necessary for the spring coil to be extended and positioned over the abutment member. For a spring capable of supporting an automobile boot lid or tail gate this will involve the application of very substantial amounts of force to the spring whilst it is in position in a physically confined and obstructed location. It is difficult to introduce into the space concerned the machinery necessary to achieve this and there is also the risk that a spring may escape as it is being extended and cause damage to the vehicle or risk of injury to the assembly workers as it lashes back.
Furthermore, it is not appropriate for springs of this nature to be painted because the paint will inevitably flake as the spring is repeatedly flexed in use. Accordingly, such an installation has to be carried out after the vehicle itself has been painted and there is thereby an extra danger of damage to the paint work of the vehicle during the spring installation. These practical difficulties have effectively caused the use of this type of spring to be abandoned or ignored and have caused the industry to put up with difficulties of the alternatives discussed above.